How to minimize TEWI: case history with oil free centrifugal chillers using R1234ze(E) refrigerant.

Object of this project was the huge renovation on an existing shopping mall in Täby (Sweden) with the aim to drastically cut down the energy consumption and CO2 emissions of the building reducing as much as possible the TEWI (Total Equivalent Warming Impact) of the installation.

We proposed to use 2 water cooled oil free centrifugal chillers with R1234ze(E) refrigerant with the double target to reduce direct impact (thanks to the use of HFO) and indirect impact (thanks to the energy efficiency and flexibility of these units).

Primarily we optimized the circuit efficiency working on the heat exchangers and unit design according with the thermodynamic properties of R1234ze(E) and secondarily we worked with consultants and designers to enhance the control strategy of the HVAC system through continuous web monitoring of working parameters and performances. A comparative analysis with standard technology is provided.

本项目的实施对象为瑞典塔比（Täby）的一座现有大型购物中心，改造目标为大幅降低该建筑的能源消耗与二氧化碳排放量，尽可能压低其设施的总等效温室效应潜值（Total Equivalent Warming Impact，TEWI）。

我们提出采用2台搭载R1234ze(E)制冷剂的水冷式无油离心式冷水机组，以期实现双重减排目标：通过使用HFO类制冷剂降低直接环境影响，同时依托该类机组的高效性能与运行灵活性降低间接环境影响。

首先，我们结合R1234ze(E)的热力学特性优化了换热器与机组设计，以提升回路能效；其次，我们协同咨询方与设计师，通过对运行参数与机组性能的持续在线监测，优化了暖通空调（Heating, Ventilation and Air Conditioning, HVAC）系统的控制策略。本项目还提供了与标准技术的对比分析。